Golf balls, which are commercially selling, are typically classified into thread wound golf balls and solid golf balls. In the solid golf balls, a two-piece solid golf ball composed of a core and a cover covering the core, and a multi-piece solid golf ball, such as a three-piece solid golf ball comprising an intermediate layer between the core and the cover of the two-piece solid golf ball, generally occupy a greater part of the golf ball market. The multi-piece solid golf ball has excellent flight performance and good shot feel at the time of hitting, because of accomplishing various hardness distributions as compared with the two-piece golf ball.
For example, a three-piece solid golf ball comprising a two-piece core composed of a core and an intermediate layer, which is formed from vulcanized rubber material having the same composition as the core of the two-piece solid golf ball, is suggested in Japanese Patent Kokai publications Nos. 228978/1990, 332247/1996, 322948/1997, 216271/1998 and the like. These golf balls are characterized by making a thickness of an intermediate layer to relatively thicker, that is, not less than 1.5 mm. The golf balls are, however, classified into two depending on whether the intermediate layer is harder or softer than an inner core.
In the three-piece solid golf balls described in Japanese Patent Kokai publications Nos. 228978/1990 and 332247/1996, of which the intermediate layer is harder than the inner core, the flight performance is excellent, but the shot feel is poor, because the intermediate layer is thick and hard. Therefore, the golf balls have very soft core in order to accomplish soft and good shot feel. However, in the golf balls, the shot feel when hit by golfers who swing the golf club at low head speed is hard and poor, if the shot feel when hit by golfers who swing the golf club at high head speed is designed to be soft and good. On the other hand, the shot feel when hit by golfers who swing the golf club at high head speed is heavy and poor, if the shot feel when hit by golfers who swing the golf club at low head speed is designed to be soft and good.
In the three-piece solid golf balls described in Japanese Patent Kokai publications Nos. 322948/1997 and 216271/1998, of which the intermediate layer is softer than the inner core, the rebound characteristics are largely degraded, which reduces the flight distance when hit particularly by golfers who swing the golf club at low head speed.
The three-piece solid golf balls are designed to accomplish high launch angle and low spin amount in order to improve the flight distance. However, since each layer in the golf ball has different deformation process on impact, a desired spin amount is not always obtained. Therefore it has been a problem that the golf ball creates blow-up trajectory or drops, which reduces the flight distance.